Image processing-based real-time displacement monitoring methods using smart devices

Displacement measurement is one of the most important methods for structural health monitoring. However, because of high cost and heavy on-site installation, conducting displacement measurement using conventional sensors is not easy in practice. In this case, with improvements in image sensors in smart devices, it seems possible to measure displacement using image processing methods. In this study, smart device-based bridge displacement monitoring system was developed. Images captured by the image sensor are processed in real time to obtain the feature-responsive displacement. First, shaking table tests based on sine wave loading were conducted so that the reliable domain for frequency and amplitude measurement for different smart devices were identified by comparing with the reference-accurate displacement sensor. Then, on-site application and stability of the proposed system were demonstrated through 1-day field measurement on a real in-service bridge. Comparison of the displacement due to traffic and temperature using smart devices with accurate displacement sensor shows significant potential of the proposed approach.